1. Field of the Invention
The field of the invention is that of small-sized electromagnetic antennas which, depending on their geometry, are capable of working at frequencies of some hundreds of MHz to some GHz.
More specifically, the invention relates to a small-sized plane printed-circuit antenna.
Small-sized antennas have numerous applications such as, for example, communications with mobile units (the antennas are, in this case, placed in portable radiomobile terminals working together with terrestrial or satellite-based communications networks), close-range communications (between computers or inside a building for example), for identification devices etc.
2. Description of the Prior Art
In the prior art, there are two main types of known small-sized antennas, namely:
wire antennas, of the dipole type or derived therefrom, generally working at frequencies of below 1 GHz. PA1 planar (or printed-circuit) antennas, working at frequencies of above 0.5 GHz. They are constituted by a metal patch parallel to a ground plane. The patch is also called a "patch". PA1 a first conductive element or patch substantially parallel to a ground plane, PA1 a first dielectric substrate separating said first patch from said ground plane, PA1 supply means for said antenna, PA1 at least one second patch that is substantially identical to said first patch, said second patch being superimposed on said first patch and being substantially parallel to said ground plane, PA1 a second dielectric substrate separating said first and second patches, PA1 at least one first short-circuit connects said first and second patches to each other, PA1 wherein at least one of said first and second patches comprises at least one slot. PA1 either operation at lower frequency for an antenna with given space requirement, PA1 or a reduction of the size of the antenna for operation at a given frequency. PA1 and the first free ends of the first and second patches are connected by said first short circuit.
Known examples of small-sized planar antennas include the quarter-wave antenna, the PIFA or "Planar Inverted F Antenna", the monolayer C type antenna and the H antenna.
There are two main existing drawbacks in most of the antennas proposed in the prior art: these are excessively great dimensions and an excessively small passband. In other words, the amount of space required by known antennas is as yet far too great and their passband is far too small for terminals that are becoming increasingly compact.